High frequency transmission system for railways



y 19354 E. Fl w. ALEXANDERSON HIGH FREQUENCY TRANSMISSIONSYSTEM RAILWAYS v 3 I Filed Aug. 20, 19 31 1 4 Figl. Q I

I Inventor; Ernst F W Alexahde1-soh,

His Attorney.

?atented May 14, 1935 UNITED STATES PATENT OFFICE Ernst F. W. Alexanderson, Schenectady, N. Y.,

assignor to General Electric Company, a corporation of New York Application August 20, 1931, Serial No. 558,288

11 Claims.

My invention relates to high frequency transmission systems and more particularly to systems for transmitting high frequency energy along the tracks of a railway system. Suchsystems have utility for example in connection with the problem of communication to and between moving vehicles on a railway track and of effecting desired signal and control operations.

The idea of signaling between moving vehicles on a railway system by means of radio has frequently been proposed. It has also been proposed to arrange a conductor along the track and supply high frequency oscillations to this conductor by means of an antenna arranged on a moving vehicle. -One of the objects of my invention, however, is to provide a system which avoids any substantial radiation of high fre-' quency energy into space and which at the same time substantially assimilates the conditions of radio transmission.

In accordance with my invention the conditions of radio transmission are imitated with the exception that the wave is confined to a particular course, such as the railway track, which it is caused to follow around curves, through tunnels, and the like. This is accomplished by causing the rails of the track to act in the manner of the ground in connection with the ground wave in ordinary space radio transmission and by creating along the track an artificial ether in which, together with the rails, the wave propagates.

Thus, for example, the ground wave in ordinary space radio transmission may be considered to propagate through a circuit comprising a plurality of links arranged together in a chain, each link of this chain being one-half of a wave length long. Each link comprises a capacitive path through the air carrying current in one direction and a return path through ground carrying current in the opposite direction. This complete chain of electric links travels outward from the transmitter with the velocity of light.

In accordance with my invention the track may be caused to act as ground. The capacitive path through the air is assimilated by a plurality of condensers, or other impedances, connected at spaced intervals between the rails of the track and a line conductor extending along the track, the conductor serving to connect one side of all of the impedances together. Thus the current in each link flows through one of the impedances to the line conductor and thence back through another condenser and the rails. These links travel along the system with a velocity dependent upon the capacitance of the condensers and substantially different from the velocity of light. The line and the rail thus form a transmission line the characteristics of which are adjusted, by the condensers, for efiicient transmission of energy along the track.

The system as thus arranged possesses important advantages which it is the object of my invention to provide. It will be observed that the transmission line is of a permanent structure, as distinct from systems in which a line conductor is connected to the rail through train controlled relays. All of the condensers employed are permanently connected between the rail and line conductor. In cases where extreme elimination of radiation is desired two line conductors may be employed forming opposite sides of the line the conductors being permanently connected between the two line conductors. By suitable means the line thus formed may be excited from one or both of the rails.

By utilizing the rail as the intermediary for the transmission of energy between the transmission line and vehicle the necessity for transmission of energy across wide gaps, as between a train carried antenna and line conductor is avoided, as is also the radiation of energy which results from the use of such gaps. The expense of providing special line conductors in the road bed is also avoided. The system is thus economical in construction and at the same time provides a simple and efficient means for transmitting high frequency energy along the track.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1, 2, 3, 4 and 5 represent different embodiments of my invention.

Referring to Fig. 1, I have indicated therein a pair of parallel conductors l and 2, these conductors being connected together at spaced intervals along their length by means of condensers 3. The conductor 5, for example, may be considered as a rail of the railway system upon which my invention is to be employed, and conductor 2 comprises a continuous conductor which extends along the track. The condensers 3 are connected between these conductors at regular intervals and have such capacitance that a wave induced into the transmission line comprising the conductors I and 2 propagates itself longitudinally of the line and is confined to it; that is, these condensers are so proportioned with reference to the distributed capacitance between the conductors I and 2 that practically all of the energy transfer between the two conductors occurs by virtue of these condensers with the result that there is practically no radiation into space.

If the capacitance of these condensers is too.

small the conductor 2 then acts as an antenna and radiates waves into space. If it is too large on the other hand, then the attenuation of the wave along the transmission line becomes excessive. Preferably the total capacitance of these condensers should be about ten times that of the inherent capacities between the conductors I and 2. While a comparatively close spacing of the condensers is desirable very satisfactory operation may be had by connecting four or five of these condensers between the conductors in every half wave length. When so constructed the velocity of wave propagation in the transmission line is substantially less than the velocity of light.

As thus arranged the rail I acts in the manner of ground in connection with the ground wave in spaced radio transmission, and the condensers 3,act in the manner of the natural capacitance of the air in connection with space radio transmission the upper portions of these condensers all being connected together by the conductor 2. The curve 4 thus indicates a radio wave traversing the transmission line.

Fig. 2 shows a more practical embodiment of my invention in which I have shown at 5 the two rails of a. railway system together with a conductor 2 extending along the system. The two rails are connected together at regular intervals along the track by means of a pair of series connected condensers 6 and the condensers 3 are connected between the conductor 2 and a point intermediate these condensers 6. The condensers 3, however, may be connected to the two rails in any manner desired, an important consideration being to avoid short-circuiting of the rails to currents impressed thereon by other signal systems such as the conventional block signal system commonly employed.

In this connection I contemplate by my invention that the transmission line 2 over which the high frequency oscillations are transmitted for the purposes of my invention shall comprise conductors which are arranged along the track for other purposes, such for example, as conductors used in connection with block signaling or train control and which are suspended on poles along the track. The condensers 3 may be so proportioned as to avoid any interference with signal circuits comprising said conductors and at the same time impress upon those conductors for transmission thereby currents employed in accordance with my invention. 1 y

In this figure I have shown two vehicles 1 and 8 spaced apart upon the tack 5, these vehicles being equipped with high frequency apparatus for signaling through the transmission line constructed in'accordance with my invention. This apparatus may, for example, comprise any suitable high frequencytransmitting and receiving apparatus which is arranged to be coupled with one or both of the rails of the track by means of coils which I have indicated at 9 and I0. These coils may be any suitable air cored coil arranged above the rails a distance for example of five inches and which preferably have their turns of wire extending longitudinally of the rail, whereby currents are set up in the rail longitudinally thereof. Oscillations thus induced into the rail are propagated along the track through the condensers 3 and the conductor 2 and may then be picked up by similar equipment arranged on a diiferent vehicle.

My invention is not limited to a capacitive connection between the conductor 2 and the rail or rails of the track but .on the other hand any other suitable type of impedance may be employed.

In Fig. 3 I have shown resistances I I employed in place of the condensers 3 and 6 of Fig. 2. A condenser I2, however, is connected in series with each resistance I I for the purpose of isolating the conductor 2 from the rails with respect to low frequency or direct currents which may be employed upon the conductor 2 for other purposes.

My invention further is not limited to the use of a conductor and rail as a transmission line over which the high frequency oscillations are transmitted, but on the other hand two conductors neither of which comprises therail may be employed. Such an arrangement is shown in Fig. 4 in which the transmission line comprises the conductors I3 and II which extend along the track. These conductors are connected together at regular intervals in the manner explained in connection with Figs 1, 2 and 3 through impedances comprising condensers I5 and windings IS in which oscillations for exciting the transmission line are induced. The total impedance of elements I5 and I6 should be sufliciently great to avoid excessive attenuation in the transmission line and is preferably capacitive. vThe windings I6 are placed in inductive relation with the rails in a manner similar to the windings 9 on the vehicle. Oscillations are thus excited in the rail by the windings 9 arranged on the vehicle and are then received by the windings I6 which are included in the impedance connections and are thus supplied to the transmission lines I3 and I4. At any distant point they may be received from the rail by. means of equipment arranged on a vehicle. I consider it an important feature of my invention that the transmission line is excited with oscillations derived from the rail and that the energy from the vehicle is induced into the rail since in this way any appreciable radiation into space is avoided.

In Fig. 5 I have shown an arrangement similar to Fig. 2 but in which the shunt capacitance is divided between two condensers I1 and I8 which are effectively connected in multiple, the condensers I1 being connected between conductor 2 and one rail of the track and condenser I8 is connected between conductor 2 and the other rail of the track. I have also shown the transmission line in Fig. S terminated by its surge impedance, this impedance comprising the impedance of resistances I9 and 20 considered as connected in multiple. In this way the effect of reflected waves on the line are avoided.

The arrangements shown in Figs. 1, 2, 4 and 5 are of the traveling wave type since the wave is propagated in the conductor in the manner of a space radio wave as already explained. Thus 0scillations travel along this line for great distances with little attenuation. In the arrangement of Fig. 3 the wave is more rapidly attenuated the energy being dissipated in resistances II. Such an arrangement may be desirable, however. in particular applications involving transmission over short distances.

In this application in speaking of signaling between vehicles I refer not only to signaling between separately operating vehicles but also to signaling between different points on a train, as for example, in front to rear communication on freight trains.

While I have shown particular embodiments of my invention it will of course be understood that I do not wish to be limited thereto since many modifications in the circuit arrangements and instrumentalities disclosed may be made, and I contemplate by the appended claims to cover any such modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in a railway signal system, of a track, a continuous conductor extending along the track, a plurality of impedance means of substantially equal value permanently connecting said conductor with a rail of said track at substantially uniformly spaced intervals along the track, and means for transmitting energy from a vehicle to said rail and for receiving energy from said rail, said impedance means being so designed with relation to the distributed line constants that substantially all of the energy transferbetween said rail and conductor occurs through said impedances.

2. The combination, in a railway signal system,'of a track, a continuous conductor extending along said track, condensers connected between said conductor and a rail of said track at spaced intervals along the length thereof, the capacity of each of said condensers being approximately ten times the distributed capacity of the respective proportionate section of said conductor and means on a vehicle for transferring energy between the circuit comprising said conductor and rail-and said vehicle.

3. The combination, in a railway signal system, of a track, a continuous conductor extending along said track, condensers permanently connected between said conductor and a rail of said track at spaced intervals along the length thereof, said conductor being isolated from said rail except through said condensers,.and said condensers being so designed with relation to the distributed line capacity that radiation from said line is substantially prevented and efiicient transmission of energy along said conductor is obtained, and means on a vehicle for transferring energy between the circuit comprising said conductor, condensers and rail, and said vehicle.

4. The combination, in a railwaysignal system, of track, a transmission line adapted to transxnit high frequency energy throughout the length of said track, means to transmit high frequency energy between a rail of said track and a vehicle operating thereon, and means at spaced intervals along the track to transmit energy between said rail and said transmission line whereby said line is in continuous energy transfer relation with said vehicle through said rail as said vehicle moves along the track, said means being so designed with relation to the distributed constants of said line that radiation of high frequency energy from said line is substantially prevented and that said line serves efiiciently to transmit energy received from said vehicle along the length of said track.

5. The combination, in a railway signal system,

of a track, a transmission line comprising a continuous conductor extending throughout the length of said track, a plurality of impedances, said impedances being connected between a rail of said track and said conductor at substantially regular intervals along the track, said impedances along the track being of substantially equal value, and designed with relation to the distributed constants of said line to produce desired efficiency of transfer of energy from any point along said track to any other point along said track, means for transferring energy between a plurality of points along said track through said transmission line, at least one of said points being on a vehicle moving on said track, said means including means at one of said points for supplying energy to the rail and at the other point for receiving said energy from said rail.

6. The combination, in a railway signal system, of a track, a transmission line comprising a continuous conductor extending throughout the length of said track, means for exciting said continuous conductor with oscillations from a rail of said track, and means carried upon a plurality of vehicles for transferring high frequency energy between said vehicles, said means including means on each vehicle for transferring energy between the respective vehicle and said rail whereby high frequency oscillations are supplied through said transmission line from one vehicle to another operating upon said track, said first mentioned means comprising impedance means permanently connected across said transmission line at spaced intervals along the track and designed with relation to the distributed line constants substantially to prevent radiation from said transmission line.

'7. The combination, in a railway signal system, of a track, a transmission line comprising a pair of conductors extending along said track, a plurality of impedances connected between said conductors at substantially regular intervals along the track, said impedances at different points along the track being of substantially equal value, said value being determined in accordance with the distributed constants of said line to produce desired efliciency of transfer of energy from any point along said line to other points along said line, means spaced at intervals along said track coupling said transmission line to a rail of said track, and vehicle carried means for transferring energy between the respective vehicle and said rail whereby energy so transferred is efficiently transmitted through said coupling means and said line.

8. The combination, in a railway signal system, of a track, a high frequency transmission line extending along said track, said transmission line having impedances connected in shunt therewith at spaced intervals along the track, said impedances being so designed with relation to the distributed line constants of said line that radiation of high frequency energy from said line is substantially prevented and energy is eflicient- 1y transmitted from any point on said line in either direction thereover, and means to transfer high frequency energy between said line and a vehicle operating on said track through a rail of said track.

9. The combination, in a railway signal system, of a track, a high frequency transmission line comprising a pair of conductors extending along said track, means coupling said transmission line with a rail of said track, said means also having impedance so designed with relation to the distributed constants of said line that radiation of high frequency energy from said line is substantially prevented and high frequency energy is efliciently transmitted from any point on said line in either direction over said line, and means for transmitting energy between a vehicle and said rail.

10. The combination, in a railway signal system, of a track, a transmission line comprising a continuous conductor extending along said track, impedance means connected at spaced intervals along the track between said conductor and a rail of said track having impedance so designed with relation to the distributed line constants that radiation of high frequency energy from said line is substantially prevented and high frequency energy is efiiciently transmitted along said line, and means for transferring said high frequency energy between a vehicle and said rail.

11. The combination, in a railway signaling system, of a track, a line conductor extending along said track, a plurality of condensers connected at intervals along said track between a rail of said track and said line conductor, said condensers having substantially equal capacitance, said capacitance being of such value that high frequency energy is transmitted by said rail and line conductor along said track with a velocity substantially less than the velocityof light, and means to supply said high frequency energy to said line conductor through a rail of said track.

ERNST F. W. ALEXANDERSON. 

